Characterization and quantitation of urinary metabolites of 2-monochloropropane-1,3-diol (2-MCPD) in Wistar rats

Fatty acid esters of 2-monochlorpropane-1,2-diol (2-MCPD) are process contaminants formed during the heat treatment of foodstuffs containing fat and salt. The limited information on 2-MCPD metabolism hinders investigating the mechanisms of toxic effects observed in skeletal and heart muscle as well as kidneys of rats treated with 2-MCPD dissolved in water by gavage over 28 days. The aim of the present work was to expand the scheme of 2-MCPD metabolism in rats. After oral administration of [¹³C₃]2-MCPD (30 mg/kg bodyweight; bw) or 2-MCPD (3 or 30 mg/kg bw) by gavage, urine samples were collected between 0 and 8 h, 8-24 h and 24-48 h. Novel metabolites were identified by ¹³C nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS), and the most abundant metabolites were quantified by isotope-dilution GC-MS and UPLC-MS/MS. The main compounds were 2-MCPD itself and the oxidation product 2-chlorohydracrylic acid (2-ClHA). Eight metabolites were detected for the first time. Products of conjugation reactions were 2-MCPD sulfate and 2-MCPD glucuronide. Six metabolites formed after degradation of glutathione conjugates were thiodiglycolic acid (TDGA), thionyldiglycolic acid (TNDGA), 3-(S-carboxymethyl)mercaptolactic acid (CMMLA), S-(carboxymethyl)-CysGly (CMCG), N-acetyl-S-(1-carboxy-2-hydroxyethyl)-Cys (CHEMA), and 2-[(2-carboxy-2-oxoethyl)sulfanyl]hydracrylic acid (2-COSHA). The mean excretion ratios of four main compounds quantified in male (m) and female (f) urine collected over 48 h following the low dose administration of 3 mg/kg bw were: 2-MCPD itself (m: 12.5%, f: 11.6%), 2-ClHA (m: 30.4%, f: 26.0%), TDGA (m: 8.5%, f: 8.1%) and 2-MCPD sulfate (m: 0.19%, f: 0.23%). In summary, the metabolites covered at least 51.6% (m) or 45.9% (f) of the dose, which allowed proposing a comprehensive scheme of metabolic pathways. Given that 2-MCPD and each of its metabolites may exert a toxic effect, two pairs of metabolites stand out due to their reactivity with glutathione: 2-chloroacetaldehyde/2-chloroacetic acid as well as 2-chlorolactaldehyde/2-ClHA.